In recent years, in the field of laser processing, there have been many attempts to use a semiconductor laser or a laser diode such as a fiber laser or a YAG laser, which has been used mainly in an excitation light source, directly in a laser processing light source as a direct diode laser (DDL). DDL is roughly divided into that of an array method which uses a combination of a plurality of bar-shaped LD arrays formed monolithically by arranging a plurality of LDs in a horizontal row and that of a single emitter method which uses a combination of a plurality of single LD chips or single emitters LDs. In either system, laser beams emitted simultaneously by a plurality of LDs are combined into a bundle of beams and are usually provided to applications such as laser processing through an optical fiber.
In the array method, generally a plurality of LD arrays are stacked to form a stacked LD module and provides a bundle of combined laser beams directly from the LD module. This method appears to be an efficient method since laser beams emitted from individual LDs are combined into one bundle immediately after emission. However, in fact, since the emission surface size of the entire LD array or the entire LD module is large, the accuracy of collimation and concentration of the combined laser beams is low. Moreover, since individual beams interfere with each other, coupling efficiency is not so high. Thus, the array method is disadvantageous.
In contrast, in the single emitter method (for example, see Non-Patent Documents 1 and 2), a plurality of single emitters LDs are arranged discretely at desired distances, and single laser beams emitted respectively from these single emitters LDs are collimated individually in a fast axis direction and a slow axis direction. Subsequently, the single laser beams are combined into a bundle in a non-contacting manner so as not to cause mutual interference. Therefore, the single emitter method is advantageous in obtaining a high-power and high-brightness laser beam.